Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Review
. 2010 Mar:31 Suppl:S21-6.
doi: 10.1016/j.placenta.2009.12.023. Epub 2010 Jan 15.

Review: Marsupials: placental mammals with a difference

M B Renfree  1
Affiliations
Review

Review: Marsupials: placental mammals with a difference

M B Renfree. Placenta. 2010 Mar.

Abstract

The placenta is the most varied organ within the Mammalia. There are many similarities, as well as some differences, between the marsupial embryo and those of eutherian mammals. The most striking difference is the lack of the inner cell mass in the blastocyst which consists solely of a single layer of trophoblast cells. The trophoblast expands and eventually becomes part of the definitive chorio-vitelline placenta. The degree of functional differentiation between the vascular and non-vascular parts of the yolk sac placenta differs between species in the relative surface area that is attached to the endometrium, in trophoblast thickness, in yolk sac fusion with the luminal epithelium and most markedly in the degree of invasiveness. In marsupials, placental physiology has been best studied in the tammar wallaby. Despite the lack of invasion in the tammar, there is nevertheless maternal recognition of pregnancy in response to trophoblast formation. Contrary to popular opinion, the tammar placenta also elaborates hormones: at term it secretes prostaglandin F2alpha and accumulates cortisol, and it expresses genes for hormones such as growth hormone, IGF2 and relaxin. As in eutherian mammals, genomic imprinting is important for placental function. Despite the relatively short period of placentation, it is clear that the trophoblast and the placenta it forms are as important for successful pregnancy in marsupial as in eutherian mammals. Marsupials are certainly placental mammals. However marsupials have an additional trick in their pouches, with the physiologically sophisticated and extended lactation that has allowed them to exchange the umbilical cord for the teat.

PubMed Disclaimer

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

Publication types

LinkOut - more resources